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Subjects

Abstract

Low atmospheric carbon dioxide (CO2) concentration1 during the Little Ice Age has been used to derive the global carbon cycle sensitivity to temperature2. Recent evidence3 confirms earlier indications4 that the low CO2 was caused by increased terrestrial carbon storage. It remains unknown whether the terrestrial biosphere responded to temperature variations, or there was vegetation re-growth on abandoned farmland5. Here we present a global numerical simulation of atmospheric carbonyl sulfide concentrations in the pre-industrial period. Carbonyl sulfide concentration is linked to changes in gross primary production6 and shows a positive anomaly7 during the Little Ice Age. We show that a decrease in gross primary production and a larger decrease in ecosystem respiration is the most likely explanation for the decrease in atmospheric CO2 and increase in atmospheric carbonyl sulfide concentrations. Therefore, temperature change, not vegetation re-growth, was the main cause of the increased terrestrial carbon storage. We address the inconsistency between ice-core CO2 records from different sites8 measuring CO2 and δ13CO2 in ice from Dronning Maud Land (Antarctica). Our interpretation allows us to derive the temperature sensitivity of pre-industrial CO2 fluxes for the terrestrial biosphere (γL = −10 to −90 Pg C K−1), implying a positive climate feedback and providing a benchmark to reduce model uncertainties9.

Plummer, C. T.et al.An independently dated 2000-yr volcanic record from Law Dome, East Antarctica, including a new perspective on the dating of the 1450s CE eruption of Kuwae, Vanuatu. Clim. Past8, 1929–1940 (2012).

Acknowledgements

This work was undertaken as part of the Australian Climate Change Science Program, funded by the Australian government—Department of the Environment, the Bureau of Meteorology and CSIRO. We thank S. Coram, R. Gregory, D. Thornton and D. Spencer of CSIRO for their analytical support and S. Allin for ice handling. W. Sturges recognizes the CSIRO Fröhlich Fellowship for supporting a visit to CSIRO, Aspendale. P.J.R. was supported by an Australian Professorial Fellowship (DP1096309). M.R.’s visit to CSIRO and D.M.E.’s visit to the Second University of Naples were supported by the Italian POLIGRID project (CUP B65B0900002007). The DML ice was sampled using funding from the Natural Environment Research Council (grant NE/F021194/1). We thank the British Antarctic Survey for providing DML ice samples. The Australian Antarctic Science Program and ANSTO supported drilling of DSS0506 through the AINSE grant and AAS grants 4061 and 3064. We thank P. Fraser for useful comments.

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Contributions

D.M.E. conceived the study. D.M.E. and M.R. planned the project. D.M.E., A.M.S., M.A.J.C., R.M. and W.T.S. sampled, dated and provided ice cores. M.R., D.M.E., C.E.A., R.L.L. and L.P.S. carried out the measurements. C.M.T. developed and ran the firn modelling and the KFDD. P.J.R., M.R., C.M.T. and D.M.E. developed the COS model and interpreted the results. I.E., M.R., D.M.E. and C.M.T. performed the carbon sensitivity to temperature analysis. All authors contributed to results interpretation and manuscript writing.